Fuel injection pump with an injection adjuster piston used to adjust the onset of injection

ABSTRACT

A fuel injection pump for adjusting the injection onset by an injection adjuster piston. The piston is embodied as a follower piston of a control slide disposed in the piston on one side the piston encloses a work chamber and is acted upon by the pressure in this work chamber counter to the force of a restoring spring, and is connected to a substantially stationary part of a cam drive of the fuel injection pump. To avoid feedback of pressure surges on the control slide and its adjustment, the inlet cross section of the connecting line is embodied as an elongated cross section extending in the displacement direction of the control slide. A more problem-free adjustment of the control slide is thus obtained, and hence also a more-precise, vibration-free adjustment of the injection adjuster piston and of the injection onset is obtained.

PRIOR ART

The invention is based on a fuel injection pump including an injectionadjuster piston used to adjust an onset of injection. In one such fuelinjection pump, known from German Patent Disclosure DE-A1 35 32 715, anaxially parallel blind bore that begins at the face end of the injectionadjuster piston remote from the work chamber is provided as a connectingline between the work chamber and the cylinder bore; on its end, thisblind bore is intersected by a transverse bore extending radially fromthe outside to the cylinder bore. The cross section of this transversebore where it enters the cylinder bore has a circular area.

In this kind of injection adjusting device, the problem arises thatbecause of the load change in the cam drive of the fuel injection pump,pressure fluctuations occur in the region of the pressure chambers ofthe injection adjuster, or relative motions between the injectionadjuster piston and the control slide.

ADVANTAGES OF THE INVENTION

By means of the fuel injection pump of the invention, the advantage isattained that when relative displacements of the control slide occur,initially only a small cross-sectional area is opened, which for thesame adjustment distance is smaller than the usual cross-sectional areaestablished when the inlet cross section of the connecting line into thecylinder bore is circular. Thus, whenever because of relative motionbetween the injection adjuster piston and the control slide, the controlslide is briefly adjusted out of its intrinsically correct positionrelative to the injection adjuster piston, only a very small throttlingcross section is opened up, so that the mispositioning of the controlslide is not immediately as a substantial change in pressure in the workchamber of the injection adjuster piston. This averts a fast, forcefulreaction on the part of the injection adjuster piston to the briefmispositioning of the control slide in such a way that incorrectvibrating or oscillating positions of this kind cannot be amplified tocause further vibration or oscillation of the injection adjuster piston.

Advantageous refinements of the embodiment of the inlet cross section ofthe connecting line into the cylinder bore are recited hereinafter. Itis essential to attain a quasi-continuous course of the cross sectionwith a steady adjustment of the control edge that controls this crosssection; the increase in cross section is effected over a relativelylong adjustment distance. In the open position, the full overflow crosssection is then available, so that in an intentional adjustment of thecontrol slide, a correction of the injection adjuster piston positioncan be made with the requisite speed.

In a further advantageous feature, the adjustment of the control slideis effected in a manner known per se by means of an actuator, which in apart of the injection adjuster structurally connected to the housingencloses a pressure chamber with a surface acted upon by the controlpressure. Because of this pressure chamber accommodated outside theinjection adjuster piston, a decoupling of this pressure chamber fromthe pressure fluctuations in the work chamber of the injection adjusterpiston is achieved, especially by means of the relief chamber locatedbetween the two. This provision as well, in a supplement to theembodiment defined herein, contributes to reducing pressure oscillationsof the injection adjuster piston.

BRIEF DESCRIPTION OF DRAWINGS

Different exemplary embodiment of the invention are shown in the drawingand will be described in further detail below.

FIG. 1 shows a section through a fuel injection pump of the distributortype with radially located pump pistons and a device for injection onsetadjustment, in the embodiment according to the invention;

FIG. 2 illustrates a cross section of an elliptical inlet;

FIG. 3 illustrates a cross section of a parabolic inlet; and

FIG. 4 illustrates a cross section of a hyperbolic inlet.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

The fuel injection pumps of the distributor type may be provided withpumps either in the form of an axially driven pump piston acting as botha distributor and a pump piston, or with radial pistons which radiallyfeed into a feed conduit disposed in a distributor. One such so-calledradial piston pump of the known type is shown in section in FIG. 1. Fourpump pistons 1 are provided, which are supported tightly displaceably inradial bores 3 of the distributor 2, at the same angular spacing in thesame radial plane to the axis of the distributor 2. On one face end, thepump pistons enclose a common pump work chamber 4, which in a knownmanner, not shown in further detail here, is filled with fuel in theradially outward stroke of the pump pistons 1, and in the radial inwardstroke of the pump pistons is made to communicate via a pressure line,also not visible here, with a distributor opening at the jacket face ofthe distributor 2; the distributor opening opens up injection lines thatoriginate at the circumference of the distributor, each of which issupplied with fuel brought to injection pressure when the pump pistonsare moving inward. By means not shown in further detail, the distributoris driven to rotate by a drive shaft in such a way that on the one handthe distributor opening is capable of performing its control functionand on the other the pump pistons are moved in the circumferentialdirection. Roller tappets 6 rest on the side of the pump pistonsopposite the pump work chamber 4 and follow a cam path 7 that isdisposed on a cam ring 8, on its annular surface pointing inward towardthe distributor. The cam ring 8 represents the substantially stationarypart of the cam drive of the pump pistons. While the device, which movesthe pump pistons and which for instance may be the ring that guides theroller tappets 6 and is coupled to the drive shaft, represents themoving part of the cam drive. Depending on the position of the cam ring,which is guided with its cylindrical outer wall in a correspondingcylindrical recess 10 of the pump housing 11 of the fuel injection pump,an earlier or later runup of the rollers 12 of the roller tappets 6 ontothe respective cam 13 is brought about, the cams being arranged suchthat all the roller tappets are moved synchronously inward or outward bythe same stroke lengths. With the adjustment of the cam ring, the onsetof the supply stroke of the pump pistons and thus the injection onsetare thus varied in proportion to the drive of the fuel injection pump.

For the adjustment, the cam ring 8 has a lug 14, which engages a recess15 in an injection adjuster piston 16, on the cylindrical jacket facethereof. The injection adjuster piston is tightly displaceable in acylinder 17 and with one face end 18 and the closed end of the cylinder17 it encloses a work chamber 20, while with its opposite other endface, in the likewise closed cylinder there, it encloses a springchamber 22. Disposed in this spring chamber is a restoring spring 23,which is supported at one end on a closure part 24 that closes off thecylinder 17 and on the other on the face end 21 of the adjusting piston16 and, thus fastened in place, seeks to cause one face end 18 of theinjection adjuster piston 16 to contact the wall 25 that closes thecylinder 17 opposite it.

Also provided in the injection adjuster piston 16 is an axial blind bore27, in the form of a cylinder bore that guides a control slide 28 andopens toward the spring chamber 22. With one face end 29 and the closedend of the cylinder bore, the control slide 28 inserted into the springchamber encloses a chamber 30, in which a compression spring 36 axiallyloads the control slide, and with its other end protrudes into thespring chamber 22, where it is acted upon by a control spring 31 that onthe other end is likewise supported on the closure part 24.

Extending in the adjusting piston parallel to the cylinder bore 27 is aconnecting line 32, which begins on one face end 18 and discharges intothe cylinder bore radially in the region of overlap by the controlslide. This discharge point can be closed by an annular collar 33 of thecontrol slide; this annular collar separates an annular groove 34located toward the work chamber from an annular chamber 35, and apressure fluid inlet discharges into the annular groove 34 while theannular chamber 35 discharges into the spring chamber 32, which isrelieved via a relief line, not shown. The annular edges defining theannular collar are control edges, by means of which, upon a relativedisplacement of the control slide, the connecting line 32 is either madeto communicate with the pressure fluid inlet 39 via the annular groove34 or relieved via the annular chamber 35 toward the spring chamber 22.The annular groove 34 is constantly in communication with the pressurefluid inlet 39, which is supplied with pressure fluid from a pressurestorage chamber 40. To supply the storage chamber, a fuel pump 41 with aparallel-connected pressure control valve 42 is used; by them togetherthe pressure storage room is supplied in a known manner with a pressurethat increases substantially as a function of rpm with increasing rpm ofthe fuel injection pump or of the associated internal combustion engine.

The adjustment of the control slide is effected with the aid of a tappet49, with which the control slide is coupled under the influence of thecompression spring 36, so that on the end of the control slideprotruding into the spring chamber 22, the control slide comes intocontact with the tappet 49. The tappet extends coaxially to the axis ofthe adjusting piston 16 or of the control slide 28, and on the sideopposite the face end 21 of the control slide, it enters an axial bore52 provided in the closure part 24. A closed work cylinder 53 isdisposed in the closure part 24; it coaxially adjoins the axial bore 52,and on its other end is closed by a cap 54. In the work cylinder, apiston 55 embodied on the end of the tappet 49 is displaceably disposed;on one end, pointing toward the spring chamber 22, it encloses apressure chamber 56, and on its other end, between the piston 55 and thecap 54, it encloses a relieved chamber 57, which via an axial bore 44,which changes over into a transverse bore 45 and communicates constantlywith the spring chamber. Also connected to the tappet 49 in the regionof the spring chamber is a spring plate 58, between which and theclosure part 24 a control spring 31 is supported, against which thetappet 49 is displaced under the influence of a control pressureintroduced into the pressure chamber 56. The aforementionedrpm-dependent pressure serves as the control pressure.

In a displacement to the right of the control slide by the tappet 49,which occurs as the control pressure rises, the annular collar 33executes a controlling function such that the work chamber 20 issupplied with pressure fluid until such time as the connecting line 32,which was previously opened, is closed again by an ensuing motion of theadjusting piston 16 counter to the force of the spring 23. Conversely,if the pressure in the pressure chamber 56 drops, the work chamber 20 isrelieved until such time as the connecting line is closed again. Thepressure in the pressure chamber 56 may also be relieved or modified bymeans of a relief line 43, in which an electrically controlled valve 44is seated.

In this known device for injection onset adjustment, the problem arisesthat via the rollers 12, feedback forces upon drive of the pump pistonsare transmitted to the cam ring 8, and the are carried in turn to theinjection adjuster piston 16, so that the pressure in the work chamberincreases in surges. This pressure is then also applied to the annularcollar 33, by way of which, upon oscillatory motions of the controlslide relative to the injection adjuster piston, fuel can also get intothe chamber 20 and cause increases in pressure there, which in turn havefeedback effects on the position of the control slide. This leads to anunstable behavior of the injection adjuster piston or of the entiredevice for injection onset adjustment.

To avoid these disadvantages, the entry 60 of the connecting line 39into the cylinder bore 27 is provided with an elongated, preferablyelliptical cross section with its main length located in thedisplacement direction of the control slide, so that upon a displacementof the control slide relative to the injection adjuster piston, by meansof the control edge of the annular collar at first only a smallthrottling cross section toward the work chamber 20 is opened up. Thus;if vibration or oscillation occurs, only a slight amount of pressurefluid can be delivered to the work chamber 20 or removed from it. Thissubstantially reduces the tendency to vibration in response to suchdisturbing forces as engine surges. Instead of an elliptical crosssection, other cross-sectional courses that reinforce this action may berealized at the opening of the inlet cross section of the pressure fluidinlet. To that end, composite parabola segments 60' as shown in FIG. 3;or hyperbola segments 60" as shown in FIG. 4 can be named, or otherboundaries of the cross sectional area in the form of conical sectioncurves.

This feature is especially advantageous in conjunction with the pressurechamber 56 structurally connected to the housing as described above andlocated outside the injection adjuster piston. With this arrangement,the occurrence of vibration or oscillation in response to impactstransmitted by the cam drive is additionally avoided, since thispressure chamber, via the relieved spring chamber, is uncoupled from theimpact-encumbered pressure side and the resultant motions of theinjection adjuster piston.

The foregoing relates to preferred exemplary embodiments of theinvention, it being understood that other variants and embodimentsthereof are possible within the spirit and scope of the invention, thelatter being defined by the appended claims.

We claim:
 1. A fuel injection pump having an injection adjuster piston(16) that serves to adjust an onset of injection, said piston operatesin a cylinder (17) that defines a work chamber (20) that is acted uponby a controllable pressure fluid that adjusts an injection adjusterpiston counter to a restoring force, a control slide (28) is disposeddisplaceably in an axial direction of the injection adjuster piston (16)in a cylinder bore (27), the cylinder bore is closed on one end, of theinjection adjuster piston (16) and is adjustable by a control pressurecounter to a force of a control spring (31), and which with controledges in the cylinder bore (27) controls a communication of a connectingline (32) from the cylinder bore (27) to the work chamber (20) with apressure fluid inlet (39) into the cylinder bore (27) or a pressurefluid outlet (35) out of the cylinder bore, the inlet cross section (60)of the connecting line (32) into the cylinder bore (27), controlled bythe control edge of the control slide (28), is embodied as an elongatedcross section extending in the displacement direction of the controlslide.
 2. A fuel injection pump in accordance with claim 1, in which thecross section is embodied elliptically.
 3. A fuel injection pump inaccordance with claim 1, in which the cross section is embodiedparabolically.
 4. A fuel injection pump in accordance with claim 1, inwhich the cross section is embodied hyperbolically.
 5. A fuel injectionpump in accordance with claim 1, in which an actuator (49, 55) effectingan adjustment of the control slide (28) has a surface acted upon by thecontrol pressure, and the actuator (49, 55) protrudes with this surfaceinto a pressure chamber (56) that is separate from the work chamber (20)and is disposed in a part (24) structurally connected to the housing,and a relief chamber (22) is disposed between the pressure chamber (56)and the work chamber (20) of the injection adjuster piston (16), whichrelief chamber is defined by the face end (21) of the injection adjusterpiston (16), and the work chamber (20) is disposed on the side of theinjection adjuster piston (16) opposite the relief chamber (22).
 6. Afuel injection pump in accordance with claim 2, in which an actuator(49, 55) effecting an adjustment of the control slide (28) has a surfaceacted upon by the control pressure, and the actuator (49, 55) protrudeswith this surface into a pressure chamber (56) that is separate from thework chamber (20) and is disposed in a part (24) structurally connectedto the housing, and a relief chamber (22) is disposed between thepressure chamber (56) and the work chamber (20) of the injectionadjuster piston (16), which relief chamber is defined by the face end(21) of the injection adjuster piston (16), and the work chamber (20) isdisposed on the side of the injection adjuster piston (16) opposite therelief chamber (22).
 7. A fuel injection pump in accordance with claim3, in which an actuator (49, 55) effecting an adjustment of the controlslide (28) has a surface acted upon by the control pressure, and theactuator (49, 55) protrudes with this surface into a pressure chamber(56) that is separate from the work chamber (20) and is disposed in apart (24) structurally connected to the housing, and a relief chamber(22) is disposed between the pressure chamber (56) and the work chamber(20) of the injection adjuster piston (16), which relief chamber isdefined by the face end (21) of the injection adjuster piston (16), andthe work chamber (20) is disposed on the side of the injection adjusterpiston (16) opposite the relief chamber (22).
 8. A fuel injection pumpin accordance with claim 4, in which an actuator (49, 55) effecting anadjustment of the control slide (28) has a surface acted upon by thecontrol pressure, and the actuator (49, 55) protrudes with this surfaceinto a pressure chamber (56) that is separate from the work chamber (20)and is disposed in a part (24) structurally connected to the housing,and a relief chamber (22) is disposed between the pressure chamber (56)and the work chamber (20) of the injection adjuster piston (16), whichrelief chamber is defined by the face end (21) of the injection adjusterpiston (16), and the work chamber (20) is disposed on the side of theinjection adjuster piston (16) opposite the relief chamber (22).